This invention is related to the field of use of image processing. More particularly, this invention is directed to a method for reducing row noise from complementary metal oxide semiconductor (CMOS) sensors.
Video and still image capture using a digital camera has become very prevalent. Video capture may be used for such applications as video conferencing, video editing, and distributed video training. Still image capture with a digital camera may be used for such applications as photo albums, photo editing, and compositing. Many components of hardware and software need to work seamlessly to both get the video data (also referred to as a video xe2x80x9cstreamxe2x80x9d) or the still image data from the hardware through the various layers of software on the personal computer (PC) and made visible on a display medium such as a monitor.
In digital cameras, a light sensitive sensor is used to capture the image that is formed on an array of light sensitive elements on the sensor through the use of a lens. Each light sensitive element on the sensor generates signals in response to the portion of the image to which it is exposed, and outputs these signals for storage or processing by post-capture circuitry. One type of sensor that is used in cameras is based on charge-coupled device (CCD) technology. Another type of sensor that may be used is based on a complementary metal oxide semiconductor (CMOS) technology. CCD sensors have been on the market for a longer period of time than CMOS sensors, but as it is generally easier to provide additional circuits on the same substrate on which the CMOS sensor is formed, CMOS sensors are becoming more popular.
CMOS sensors suffer from row noise, which manifests itself in forms of light or dark stripes appearing at different locations in any captured images. The position of these stripes are not the same from one frame to the next. Thus, in a sequence of frames captured by a CMOS sensor, such as in a video sequence, stripes will appear at random during playback of the displayed image. Similarly, in a series of captured images where each captured image is a xe2x80x9cstillxe2x80x9d image, row noise appears at different positions from one image to the next. This row noise typically is caused by a random amount that is added to the intensities of the pixels for each row in a captured image. These random amounts, whether positive or negative, are referred to as random offsets.
The row noise described above is different from fixed pattern noise, which is noise that appear in the same position in every frame or captured image. For example, a single light sensing element (i.e., a pixel) in a CMOS sensor may be deficient in its sensitivity or output level, which produces a consistent undervalued output for that pixel location in each captured image. These fixed pattern noises may be detected and compensated for either during the manufacturing process or during the post processing of captured images. Row noise cannot typically be corrected during the manufacturing process, so other means must be used to correct them.
A method including determining a set of row sums for a set of pixel rows and a set of corresponding contributing pixel counts. The method also including determining a set of row offset corrections; and, adjusting the set of pixel rows by the set of row offset corrections.